Dynamic voltage and frequency scaling (DVFS) is a technique to reduce power consumption by dynamically controlling supply voltage and an operating frequency of a processor depending on a load.
There has been known a power supply device of a step-down DC-DC converter having a power semiconductor switching element, a driving unit for the power semiconductor switching element, a pulse-width modulating oscillator supplying a drive signal to the driving unit, and an error amplifier supplying an error signal to the oscillator (see, for example, Patent Literature 1). The power supply device has a power system output filter passing output power and a filter provided separately from the power-system output filter, and feeds back an output signal to the error amplifier by directly coupling an output of the separately provided filter and a differential amplifier in the error amplifier.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2004-80985
To adjust supply voltage corresponding to a load fluctuation of the processor, a switching frequency equal to that of the reference clock signal of the processor is needed. Accordingly, a high-speed DVFS is desired. However, when the switching frequency changes depending on the load of the processor, it is difficult to supply large power to the processor.